The invention relates to an electric motor intended to be fixed to a printed circuit board.
The prior art discloses electric motors, in particular as meter mechanisms in motor vehicle display instruments, in which the coil ends of the electric motors are electrically conductively connected to pins which, in a push-through mounting operation, are electrically conductively connected to a rigid printed circuit board, for example by flow soldering. In addition, the prior art discloses electric motors which are connected to a rigid printed circuit board by means of screws. The drawback in this case is the additional, time-consuming screwing operation and the complicated securing of the screws against inadvertent loosening.
The object of the invention is therefore to provide an electric motor which can be connected simply and permanently to a printed circuit board.
The object is achieved in that the motor has at least one expanding dowel, that the motor can be fixed to a printed circuit board by the expanding dowel being expanded, and that at least one expanding dowel can be secured by a pin.
The expanding dowel can be expanded by its consisting of an elastic material and, during the mounting, being compressed for a time and led through cutouts in a printed circuit board, and subsequently being able to assume its original shape again. In this way, the motor is fixed to the printed circuit board. In order to prevent the expanding dowel being compressed again, the expanding dowel can be secured by a pin. This effectively prevents the expanding dowel being compressed again following the mounting operation.
It is also possible for the pin, on its own, to effect or at least to assist the expansion of the expanding dowel. As a result, the expanding dowel is fixed to the printed circuit board even more firmly.
Inserting the pine axially into the expanding dowels permits very straightforward mounting of the motors by pressing in the pins from a direction above the printed circuit board.
The mounting operation is simplified further if the pins are detachably connected to the expanding dowel before the mounting operation. This means that it is possible to dispense with feeding the pins separately.
The connection can be carried out, for example, via webs. In this way, the pin and the expanding dowel can be produced in one piece as an injection molding.
By means of a force acting axially on the pins, the webs then break, given an appropriate design, and the pins can then be inserted into the interior of the expanding dowels in order to secure them.
The fact that the contact springs are configured in such a way that, after the electric motor has been fixed to the printed circuit board, they are in contact under prestress with electrical conductors on the printed circuit board, means that an additional soldering operation can be dispensed with, given an appropriately corrosion-resistant material of the surfaces o the contact springs, such as tin, gold or platinum.
The configuration of the motor is particularly simple if the contact springs are fixed to the coils.
A casing, which has openings for the contact springs, and through which the contact springs protrude out of the casing, firstly projects the motor against external influences, also simplifies the mounting operation and permits direct mounting of the contact springs on the coils.
If the contact springs are configured in such a way that, after the motor has been mounted on the printed circuit board, they are in contact underneath the casing, space on the printed circuit board is also saved. In addition, the casing can then be configured in such a way that, following the mounting of the motor on the printed circuit board, the printed circuit board completely covers the openings and the casing is therefore closed. The mechanical and electrical components of the motor are thus protected better, in particular against the action of heat, for example during surface mounting of other components on the printed circuit board, needed following the mounting operation.
By configuring the contact springs in such a way that, after the motor has been mounted on the printed circuit board, they are in contact at the side of the casing, the contact spring can also be soldered to conductors on the printed circuit board during surface mounting, if particular requirements are placed on the durability of the electrical connection, In this case, the opening in the casing can be configured such that the casing largely protects the motor, so that the action of heat, arising for example from a reflow soldering operation, does not damage the motor.
A simple mounting operation for the contact springs results if the coils each have a coil former and the contact springs are fixed on or in the coil former. The mounting operation can be carried out particularly simply if the coil former is configured as an injection molding and the contact springs are encapsulated by injection molding with parts of the coil former.
A permanent electrical connection between the coil windings and the contact springs may be produced by the ends of the coil windings being electrically conductively fixed to the contact springs, for example by soldering or welding, and the contact springs then being bent over at these ends in such a way that the coil ends are relieved of stress.
A compact design of the electric motor may be achieved by the stator plates forming a stator which, at the center, has an opening to accommodate the rotor, the individual stator plates being arranged around the opening. The motor becomes particularly compact if it has four stator plates and two coils.
If two opposite stator plates are simply bent over toward each other in such a way that parts of the stator plates are aligned parallel to each other, between which the first coil is arranged in a magnetically coupled fashion, and if the two other stator plates have a first bend in the vicinity of the opening and a second bend in the vicinity of the free ends, and the second coil is magnetically coupled between the free ends, the coils can be arranged in parallel at the same height and can thus be configured identically.
If the stator plates are magnetically coupled at the openings, they can be produced together, in one piece, from a metal plate.
If the stator plates are connected to one another at the opening via a nonmagnetic metal, the motor can be driven particularly easily.
By welding coil cores of the coils to the stator plates, the coils can be magnetically coupled rapidly, permanently and effectively to the stator plates.